The Center for College Affordability and Productivity has released today a new study showing the high and increasing extent to which college graduates are working in jobs that don’t call for any particular academic preparation. Rich Vedder, Jonathan Robe, and Matthew Denhart dig into BLS data to show that many young people have “invested” in college degrees (usually with a lot of involuntary help from taxpayers) only to discover that the best employment they can find is in fields where the workers have traditionally held only high-school diplomas, if even those.

The Inside Higher Ed story on the CCAP study has the inevitable riposte from Anthony Carnevale, who never concedes an inch when defending his notion that college is a good investment for virtually everyone. He says that it can’t be true that we have a 48 percent surplus of college grads when there is an 84 percent “premium” for college-educated workers. Evidently he is unaware that Vedder and his co-authors explain exactly how that can be the case.

There is no “premium” paid to workers just on account of their higher level of education. Rather, there has been a long-term trend in the U.S. of employers’ offering higher-paying jobs only to those with college degrees. They use education credentials as a screening mechanism to legally discriminate against presumably less reliable people who did not graduate from college. As the use of the college degree as a screening mechanism spread to more and more industries, the number of entry-level jobs that remain available to those who don’t have college credentials (and hence, good career paths) has shriveled. Workers are not paid more because they managed to get a college degree, but instead those who don’t have one are increasingly limited to lower-paying work that often lacks advancement potential.

On average, it looks as though earning a college degree is a good investment, but, as Vedder argues, that average is not relevant. People need to look at the margin — the prospects today of the mass of mid- to lower-ability students who may be considering college not because they have a desire for deep learning, but because they think they need the degree to get a good job. Many of them won’t.